When creating a Reorder Analysis in Order Time, the time horizon that is selected allows you project for a certain time range in months or weeks. Based on that time horizon and other selected criteria, the data is analyzed and results are given for utilize.
You may have items that are on Sales Orders for which the promised date is not yet due until pass the horizon dates selected. Those items will not be flagged into the Reorder Analysis since they do not fall into that date range. You can expand the time horizon dates to make sure that those promised dates are included in the results that are returned.